Pentax has a number of excellent lenses and the dSLR cameras can use any Pentax lens ever made. I'm personally using a 50mm 1.7lens that I bought new in 1980, and you can use older M42 screw-mount lenses with an adaptor.

This option works well for someone who has past experience and/or already owns a lot the older K-mount equipment. To be honest, the OP here doesn't sound like the type that probably needs to be going this route.

$600 is about as rock-bottom as you can get in terms of a DSLRbody and even one good prime. I would buy a lens that fully communicates with the body vs. this adaptor+ manuallenses for the 1980's stuff. First, you'll be using stop-down metering. Do you know what that means? You would alsobe manually focusing using screens in camerasthat, quite honestly, are not easy tomanually focus with, especially in low light.

Scan the list of Canon DSLR's at a reputable online dealer, like B&amp;H...

The cheapest CanonDSLR costs $519, which leaves you $81 for a lens. Not sounding too good......

Whatever DSLR you wind up buying, you probably should be looking at a kit-lens outfit that gives you more options up front and start a savings plan for a better prime lens. It does not sound like you've really thought things through too well or done much research yourselfand are just looking for someone to point you in some direction, and you'll get plenty of that as you already have, much of which will wind up costing you way more than $600. Whether any of it is right for you or not, you'll need to figure that out.

It could also be, the OP just needs to buy a tripod and learn how to use the A720 he already owns. Knowing how to use your equipment and post processing can do more than throwing money at the equipment side of things, especially if you don't know what you want or how to use it after you buy it. Look at these A620 images and try to figure out how much better they would be ifthis guyhad just used a DSLR (which he does already own)...